The present invention relates to a novel coating method according to a two-coat one-bake coating system.
Heretofore the body panels of motor vehicles, two-wheel vehicles, electrical appliances, etc. which must have good appearance have been coated for finish with an organic solvent-diluted thermosetting top coat composition capable of forming a finish film excellent in surface smoothness, distinctness-of-image gloss, weatherability and the like. The two-coat one-bake coating system or method (hereinafter referred to as "2ClB method") has been generally employed to form such finish film. According to the 2ClB method, a substrate is usually coated with an organic solvent-diluted thermosetting enamel base coat composition containing a coloring pigment and/or metallic pigment, and an organic solvent-diluted thermosetting clear top coat composition is applied to the air-dried but uncured base coat, followed by curing the two coatings at the same time.
A demand for the improvement in the good appearance of finish film has been increased in recent years. To improve the smoothness of coating surface, measures such as the addition of rheology controlling agents, polishing of intercoats or the like have been attempted. On the other hand, since high solids coating compositions developed as antipollution measures can readily give a thick film and advantageously improve the appearance of coating film, they have been frequently used as clear top coat compositions in combination with the above base coat composition.
However, the aforementioned conventional methods have the drawbacks of increasing the number of coating steps by addition of polishing and unsatisfactorily improving the coating film appearance. Further, conventional base coat compositions contain a large amount of organic solvent, hence undesirable in view of the need for savings in resources, pollution control and the like. High solids base coat compositions alternatively available are limited in reduction of organic solvents and cause the lack of whiteness in finish film when used for a light-colored metallic coating of silver or like color.
An object of the present invention is to provide a novel coating method free of the above drawbacks of the 2ClB method.
Another object of the invention is to provide a novel coating method capable of giving coating films excellent in surface smoothness, gloss, distinctness-of-image gloss and like finishing properties as well as in adhesion, hardness, and resistance to impact, chipping, scuffing, xylol, acids, weather, water and humidity, the coating method being also advantageous in saving resources and alleviating pollution problems.
These and other objects of the invention will become more apparent from the following description.